1. Field of Invention
The invention relates to a fixing device in an image forming apparatus for fixing a toner image transcribed on paper by heating the paper transcribed with the image, which is formed by supplying a toner in accordance with an electrostatic latent image formed on a photosensitive drum in a developing device, by a heating roller. Particularly, the invention relates to a fixing device in which in bringing a cleaning member used for cleaning the heating roller into press contact with the heating roller, by setting a press-contact force of the cleaning member in respect of both end portions of the heating roller smaller than a press-contact force in respect of portions of the heating roller other than the both end portions, wear of the surface of the heating roller caused by toner, paper powder or other like contaminants and the cleaning force can be made uniform over the entire length of the heating roller.
2. Description of Related Art
There have conventionally been proposed various image forming devices, such as a laser printer or the like, adopting a so-called electronic photographing system. For example, an image forming device having a paper feeding device, a laser scanning device, a toner supplying device, a developing device, a fixing device and the like in gross classification, is disclosed in the specification and the drawings of Japanese Published Document No. 9-319201. According to such an image forming device, an electrostatic latent image is formed on the surface of a photosensitive drum in the developing device in accordance with image data presented using the laser scanning device, a toner image is formed on the photosensitive drum by supplying a toner, in accordance with the electrostatic latent image, from the toner supplying device, the toner image is transcribed by cooperation of a transcribing roller and the photosensitive drum onto a paper fed from the paper feeding device into the developing device and thereafter, the toner image is fixed by heating the paper by the fixing device.
In the fixing device, generally, a heating roller and a pressing roller, that is brought into press contact with the heating roller, are rotatably arranged. With respect to the surface of the heating roller, toner which is not fixed to the paper, paper powder generated from the paper and other like contaminants become adhered to the surface of the heating roller. A cleaning member composed of a felt member is brought into press contact with the surface of the heating roller to remove toner, paper powder and the other like contaminants adhered to the surface of the heating roller. The cleaning member is generally brought into press contact with the surface of the heating roller with a press-contact force which is uniform over the entire length of the heating roller.
In the meantime, generally, when toner, paper powder and the other like contaminants are adhered to various rollers, there is a tendency for the toner, paper powder and the other like contaminants to be aggregated at both end portions of the rollers in accordance with rotation of the rollers.
Under such conditions, when the cleaning member is brought into press contact with the heating roller with a press-contact force which is uniform over the entire length of the heating roller, as in the conventional fixing device, the toner, paper powder and the other like contaminants collected at the end portions of the heating roller operate as a polishing agent between the cleaning member and the heating roller whereby the end portions of the heating roller are polished. In this case, even at the central portion of the heating roller, the toner, paper powder and the other like contaminants operate as a polishing agent between the cleaning member and the heating roller and therefore, the central portion of the heating roller is also polished.
However, the amount of the toner, paper powder and the other like contaminants is larger at the end portions of the heating roller than at the central portion of the heating roller and accordingly, the amount of polishing of the heating roller caused by the toner, paper powder and the other like contaminants is larger at the end portions whereas it is smaller at the central portion. When the amount of polishing becomes nonuniform over the total length of the heating roller, there is the possibility of problems of an unequal fixing function caused by a nonuniformity of the fixing force in fixing the toner image formed on paper developing over time.